Process for preparing acrylonitrile polymers



United States Patent 6 PROCESS FOR PREPARING ,ACRYLONITRILE POLYMERSCharles Cliiford Keener, 'waynsnaro, Va, assigno'r to E. I. du Pont ileNemoursand Company, Wilmington; Del., a corporation of Delaware NoDrawing. Filed Feb. 5, 1957, Ser. No. 638,223

6 Claims. (Cl. 260 -63) This invention relates to an improved processfor the polymerization of acrylonitrile and more particularly to theproduction of acrylonitrile polymers and copolymers of improved heatdiscoloration characteristics while maintaining relatively high rates ofconversion.

Production of acrylonitrile polymers and copolymers has generally beencarried out by Redox polymerization, e.g. with potassium persulfate asthe catalyst or initiator and sodium metabisulfite as the activator..The ratio of activator to catalyst has been below about 2:1 to attaingood rates of conversion of monomer to polymer but under such conditionsthe polymer produced is not as color stable as is desired and filamentsand fibers pro duced therefrom have a yellowish cast. To overcome thisdeficiency it has been demonstrated that whiter polymeri'c fibers resultwhen the polymerization is carried out at relatively high ratios ofactivator to catalyst, for example, with six or eight or more times asmuch bisulfite activator as persulfate catalyst. Such processes, however, are carried out at reduced rates of conversion and when "themonomer feed is increased to maintain satisfactory production rates, theslurry of polymer becomes too thick to handle. The process of thepresent invention provides a way of producing polymer relatively stableto discoloration on heating, at satisfactory rates of conversion andwithout developing thick slurries of polymer.

Therefore, an object of this invention is to provide an improved processfor polymerization of acrylonitrile polymers and copolymers containingat least 85% acrylonitr ile to produce more color stable polymer andwithout substantial reduction in rate of conversion. Other objects willbe apparent from the description that follows.

These objects are accomplished by polymerizing acrylonitn'le monomerwith or without minor amounts of other polymerizable monomers in thepresence of a persulfate as the catalyst, a sulfoXy-reducing agent asthe activator, from 0.05% to 0.30% of ,B-mercaptoethanol, and from 0.2to 5 parts per million of iron (based on total feed to the reactor).Polymerization is carried out in aqueous medium wherein the ingredientsat the start of :the reaction or in the feeds to a continuous reactionand the reaction conditions may range in quantity as indicated in thetable below.

Percent total monomers 18.5 to 35 P.p.m. ionic iron 0.2 to 5, Percentbeta mercaptoe'thanol 0.05 to 0.3 Percent 1 activator as sodiummeta-bisulfite 2 0.2 to 3.8 Percent 1 catalyst as potassium persulfate0.2 to 0.7 Temperature C.) 45 to 60 Residence time (min.) 30- to 110Water to balance acidified with sulfuric acid to pH of 1.8 to 3.75

Based on monomers.

Stoichiometric equivalent amounts of S0 may be substituted for sodiummeta-bisulfite. If S0: is used, no acid is necessary for lowering pH.

products. A measure of the ultimate whiteness of the products canbe'preliminarily determined by measuring the color stability of thepolymer after-being heated in solution which test is termed heated colorvalue and abbreviated to HCV for convenience. This test consists in.heating a 25% solution of the polymer in pure N,N-dimethylformamide at100 C. for '4 hours and then "testing this sample, diluted to aconcentration of 5.8%

polymer, by measuring its optical density at 400 millimicrons against asample of pure solvent using a Beckman Model DU Spectrophotometer. Theoptical density times 100 is taken as the heated color value of thepolymer. The lower this value, the more stable the polymer is to heatdegradation and whiter the fiber produced therefrom by normal productionmethods' Heated color values below about 12 are considered satisfactoryfor the production of white products.

Polymerization is preferably carried out in a continuous polymerizer buta batch reactor may also be used. The process may be used in preparinghomopolymers of acrylonitrile or copolymers of acrylonitrile and anethylenically unsaturated monomer wherein the acrylonitrile content isnot less than Some copolyme'rizable ethylenically unsaturated monomersthat may be used are. vinyl acetate, methyl vinyl ketone, methylacrylate, methyl methacrylate, butyll acrylate, butyl metha crylate,dimethyl itaconate, diethyl maleate, vinyl tr'imethylace-I tate,methacr'ylonitrile, styrene, vinyl ethyl hexyl ether, styrenesulfonicacid, ethylenesulfonic acid, allylsuilfonic acid, etc. and their alkalimetal salts. Two or more copolymerizable monomers may be used asdesired.

The following example is given by way of illustration and no limitationis placed on the particular polymers or catalyst or activator, since anyacrylonitrile copolymer having at least 85 acrylonitrile content maybesubstituted for the polymers given in the example. Likewise, anyammonium or alkali metal salt may be used in place of the sodium orpotassium salt of metabisulfite and persulfate. Other sulfoxy reducingagents may be used alone or in part as the activator such as sodiumbisulfite, sodium hydrosulfite, sulfur dioxide and the like.

EXAMPLE A series of continuous polymerization runs were made. In eachcase the run was started with the overflow polymerizing kettle partlyfilled with demineralized water, acidified with sulfuric acid to a pH ofabout 3.25 and heated to a predetermined temperature. Then were addedthe monomers, and dilute aqueous solutions of potassium persulfate asthe catalyst or initiator, sodium metabisulfite as the activator,B-mercaptoethanol, iron inthe form of ferrous ammonium sulfatehexahydrate (when added) together with sullicient demineralized waterand sulfuric acid to maintain the desired concentration and a constantpH in the range of from 3.1 to 3.5. -In the table that follows thevarious percent of feeds are given together with the percent conversionof monomer to polymer, the intrinsic viscosity (1;) and HCV of thepolymer, consistency of the polymer slurry, residence time andtemperature of the reaction. In all cases each reaction mixture containsabout 0.2 part per million of iron over and above any amount of addediron.

Continuous polymerzzatzons Percent Percent Percent Percent p.p.m. Resi-Expt. Conver- HCV Cata- Activa- Percent Mono- Fe deuce Remarks sion lyst1 tor 1 ME 1 mar Added Time Feed (min.)

64. 4 8.1 0. 34 4. 0. 00 18. 0.00 53. 4 94% AN-6% MA: 0.27% BSA based onAN and MA. 83. 7 16.5 0. 57 0. 97 0. 00 30. 0 0. 00 73 94% AN-6% MA. 21.6 18.3 0.35 0.00 0. 25. 0 1.00 72.6 Same as 1 above. 78.7 8.4 0.63 1. 070. 10 30. 0 0. 00 62. 7 94% AN-6% MA: 0.23% SSA based on AN and MA. 78.9 11.0 0.50 0.353 0. 10 35. 0 0.19 65. 7 Same as 1 above. 77. 9 10. 9 0.55 3.00 0. 11 30. 0 0.90 27 94% AN6% MA: 0.33% SSA based on AN and MA.75. 5 11. 50 0. 45 3.00 0.11 30.0 0.90 2&1 Same as 6 above.

77 10. 0 0. 2 0. 2 0. 10 24. 0 0. 3 80 97.95% AN. 2.05% SSA.

1 Based on Monomer.

ME= beta mcrcaptoethanoL AN =acrylonitrile. MA=methyl acrylate.SSA=sodium styrenesuhonate.

The temperature was 45 C. in Experiment 1 and 60 C. in Experiment 7-allthe rest were carried out at 48 C.

The filtrate from Expt. 8 possessed one-tenth of the biological oxygendemand (BOD) oi the filtrate from Expt. 1.

Experiment 1 shows that good color but thick slurry consistency and lowconversion were obtianed by the use of the high ratio of activator toinitiator and without any fl-mercaptoethanol present. Experiment 2 showsgood conversion and thin slurry consistency but poor color obtained witha low ratio of activator to initiator and without any fi-mercaptoethanolpresent. Experiment 3 shows por color and poor conversion when therecipe is conducted with a small amount of B-mcrcaptocthanol and withoutactivator. Experiment 4 shows good color, satisfactory conversion andthin slurry consistency when a low ratio of activator to catalyst isused with a small amount of fi-mercaptoethanol. Experiment 5 shows thata 35% monomer feed may be used and still have a relatively thin polymerslurry, a satisfactory polymer color and good conversion even though theactivator/initiator ratio is very low when a small amount offi-mercaptoethanol is present. Experiment 6 shows good conversion,satisfactory color and thin slurry consistency'obtaiued in a short timewhen a high ratio of activator to initiator is used with a small amountof fi-mercaptoethanol. Experiment 7 shows that an elevated temperaturemay be used for a short residence time with little effect on color,conversion and slurry consistency when a high ratio of activator toinitiator is used with 0.3% B-mercaptoethanol. However, the smallreduction in conversion indicates that the higher amount ofB-mercaptoethanol offers no advantage over a small amount such as usedin Experiments 4 to 6. Experiment 8 shows that other ethylenicallyunsaturated monomers (in this case, styrenesulfonic acid) may be usedand shows the reduced amounts of ingredients (i.e., total of catalyst,

from the spirit and scope thereof, and therefore it is not intended tobe limited except as indicated in the appended claims.

I claim:

1. The method of producing substantially white acrylonitrile polymerswhich comprises polymerizing a reaction mass containing from 18.5% to35% of monomers selected from the group consisting of acrylonitrile anda mixture of ethylenically unsaturated monomers containing at least 85%acrylonitrile and up to 15% of'a copolymerizable monomer, from 0.2 to 5parts per million of a soluble iron compound calculated as Fe, from0.05% to 0.3% of beta-mercaptoethanol, from 0.2% to 3.8% of a sulfoxyreducing agent as an activator, from 0.2% to 0.7% of a persulfate as acatalyst, the balance being water, acidifying the mass with sulfuricacid until a pH of from 1.8 to 3.75 is obtained, heating the acidifiedsolution from about 30 to 110 minutes at a temperature of about 45 to 60C., and separating the polymer so formed, the percentage of thebeta-mercaptoethanol, activator and catalyst being based on the weightof the monomers.

2. The process of claim 1 in which the activator is an alkali metalmetabisulfite.

3. The process of claim 1 in which the activator is sodiummctabisulfite.

4. The process of claim 1 in which the catalyst is an alkali metalpersulfate.

5. The process of claim 1 in which the catalyst is potassium pcrsulfatc.

6. The process of claim 1 in which the iron is added in the form offerrous ammonium sulfate.

activator, p-mcrcaptoethanol and iron) possible using this invention.Experiment 8 also shows the relatively References Cited in the file ofthis Patent l g 13 1 of at si s g 1 f UNITED STATES PATENTS 1s invcn onena es e pro no 1011 0 p0 ymers o acrylonitrilc containing at least 85%acrylonitrile at good .iP j i i f g rates of conversion and with goodcolor stability with- 2743263 croyan y 1956 out having to contend withthick polymer slurries. The 48106 i ig i 1956 improved color stabilityof the polymer, which means 2777832 i fii er auer e a J W 1957 improvedwhiteness of the filaments, fibers, and the like 2793200 ""7 producedtherefrom, makes the products of this invention est May 1957 admirablysuited for all kinds of fine textiles especially OTHER REFERENCES forwhite goods or goods to be dyed in pastel shades.

It will be apparent that many widely different embodiments of thisinvention may be made without departing Thomas et al.: Journal ofPolymer Science, volume 17, pages 275-290.

1. THE METHOF OF PRODUCING SUBSTANTIALLY WHIRE ACRYLONITRILE POLYMERSWHICH COMPRISES POLYMERIZING A REACTION MASS CONTAINING FROM 18.5% TO35% OF MONOMERS SELECTED FROM THE GROUP CONSISTING OF ACRYLONITRILE ANDA MIXTURE OF ETHYLENICALLY UNSATURATED MONOMERS CONTAINING AT LEAST 85%ACRYLONITRILE AND UP TO 15% OF A COPOLYMERIZABLE MONOMER, FROM 0.2 TO 5PARTS PER MILLION OF A SOLUBLE IRON COMPOUND CALCULATED AS RE, FROM0.05% TO 0.3% OF BETA-MERCAPTOETHANOL, FROM 0.2% TO 3.8% OF A SULFOXYREDUCING AGENT AS AN ACTIVATOR, FROM 0.2% TO 0.7% OF A PERSULFATE AS ACATALYST, THE BALANCE BEING WATER, ACIDIFYING THE MASS WITH SULFURICACID UNTIL A PH OF FROM 1.8 TO 3.75 IS OBTAINED, HEATING THE ACIDIFIEDSOLUTION FROM ABOUT 30 TO 110 MINUTES AT A TEMPERATURE OF ABOUT 45* TO60*C., AND SEPARATING THE POLYMER SO FORMED, THE PERCENTAGE OF THEBETA-MERCAPTOETHANOL, ACTIVATOR AND CATALYST BEING BASED ON THE WEIGHTOF THE MONOMERS.